marinamele_add_method.py

class Day(object):
    def __init__(self, visits, contacts):
        self.visits = visits
        self.contacts = contacts

    def __add__(self, other):
        total_visits = self.visits + other.visits
        total_contacts = self.contacts + other.contacts
        return Day(total_visits, total_contacts)

    def __radd__(self, other):
        if other == 0:
            return self
        else:
            return self.__add__(other)

    def __str__(self):
        return "Visits: %i, Contacts: %i" % (self.visits, self.contacts)

day1 = Day(10, 1)
day2 = Day(20, 2)
print day1
# Visits: 10, Contacts: 1
print day2
# Visits: 20, Contacts: 2

day3 = day1 + day2
print day3
# Visits: 30, Contacts: 3

day4 = sum([day1, day2, day3])
print day4
# Visits: 60, Contacts: 6